The application of composite sandwich structures to primary structures, i.e. the aircraft fuselage, offers a high potential for weight saving and function integration and has so far only been utilized for small business jets. However, this concept poses a number of challenges to the designer, like condensing and accumulating water in the honeycomb cells resulting from the temperature difference between ground and air. Therefore, the commercial aircraft manufacturer Airbus has developed a promising concept for a sandwich fuselage named VeSCo (Ventable Shear Core). A ventable core with open cells is one of the principles of this concept, allowing for handling of the condensate, which is not possible with closed honeycomb cells. This advanced core structure is a folded core, which can be produced from almost any sheet material in a number of different geometries in a continuous process. The current study focuses on folded cores made of phenolic resin-impregnated Kevlar paper. Impact or crash simulations of the folded cores with these types of cellular structures require knowledge of the homogenized mechanical properties, since a detailed cell wall modeling approach is impracticable for large sandwich structures. One way to determine these nonlinear effective mechanical properties is extensive experimental testing under compressive, tensile and shear loading. Another way is to use detailed finite element models of the cellular core in combination with virtual material testing. In this case, a variation of geometric or constitutive parameters can easily be performed in order to optimize the structure's mechanical properties. This paper describes the development of such detailed folded core models in LS-DYNA. The parameter identification of the cell wall material and the validation of the models were performed by means of an optimization with LS-OPT with regard to basic experimental data of the core manufacturer. Merits and limits of this approach are discussed. The application of the folded core material model for drop test simulations of a sandwich fuselage barrel is briefly addressed.
Numerical determination of the nonlinear effective mechanical properties of folded core structures for aircraft sandwich panels
2007
10 Seiten, 8 Bilder, 20 Quellen
Aufsatz (Konferenz)
Englisch
Flugzeugrumpf , Sandwich-Bauweise , Faltwerk , Luftdurchlässigkeit , offene Zelle , Papier , Aramid , Phenolharz , mechanische Eigenschaft , nichtlineares System , numerisches Verfahren , mechanische Homogenisierung , Finite-Elemente-Methode , Parameterschätzung , Parameteroptimierung , Simulationsversuch , mechanischer Stoß , Materialeigenschaft
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